Exercise may put some heart patients at risk

As counterintuitive as it may sound, Peter Ruben and graduate students Colin Peters and Mena Abdelsayed have found that intense exercise is not advisable for everyone.

Last year, the team published results that showed sudden death caused by cardiac arrhythmia could be triggered by changes in body temperature in those with a particular protein mutation.

The otherwise healthy hockey player who drops dead suddenly and unexpectedly in the middle of a game, or the infant who dies during sleep, is often a victim of arrhythmia.

The team’s latest findings released in the journal, Progress in Biophysics and Molecular Biology this month, reports that increased levels of blood acid, as happens during intense exercise, may trigger a cardiac arrhythmia in certain people who carry one of several rare genetic mutations that affect proteins responsible for electrical signaling in the heart. Although the mutation is rare, Ruben notes, “One avoidable death is one too many.”

Ruben explains that blood acidosis alone can increase the risk of an arrhythmia. “Blood acid increases as a normal result of exercise through anaerobic metabolism. Anaerobic metabolism is the creation of energy when the lungs cannot provide enough oxygen to keep up with the body’s demand for energy.”

Ruben says, “A by-product of anaerobic metabolism is lactic acid, the presence of which during intense exercise may contribute to respiratory acidosis, an increase in acid (lactic acid, in this case) in the blood.”

Ruben advises people who participate frequently in intense exercise to consider being genotyped if they have a family history of sudden cardiac death. “Those who carry this genetic mutation should consult directly with their physician regarding what moderate exercise should entail and, for those with more severe cases, perhaps consider getting an implantable defibrillator.”

Since body temperature has also been shown to play a role in these events Ruben adds, “Prolonged exposure to saunas and hot tubs should probably be avoided”.

Ruben became interested in cardiac arrhythmias after researching epileptic children who had experienced febrile seizures. Such seizures are associated with high body temperatures, which led Ruben to investigate whether heat also played a role in cardiac arrhythmias.

The Natural Sciences & Engineering Research Council of Canada (NSERC) has provided funding for this research.